Employer Bullying

My wife is a dental assistant that works for two dentists at a single practice. One dentist everyone can work with without any issues but the other, no one can manage to work with for longer than a couple days because the way they are treated by her.

My wife has somehow become the only person that works with said dentist now and is constantly being bullied and treated terribly by her. Is there anything that can be done other than quitting? My wife has worked there for 7ish years and put up with it but it has become increasingly worse.